National Institute
on Alcohol Abuse and Alcoholism No. 38 October 1997

Alcohol, Violence,
and Aggression

Scientists and
nonscientists alike have long recognized a two-way association between alcohol
consumption and violent or aggressive behavior (1). Not only may alcohol consumption
promote aggressiveness, but victimization may lead to excessive alcohol consumption.
Violence may be defined as behavior that intentionally inflicts, or attempts
to inflict, physical harm. Violence falls within the broader category of aggression,
which also includes behaviors that are threatening, hostile, or damaging in
a nonphysical way (2). This Alcohol Alert explores the association
between alcohol consumption, violence, and aggression and the role of the
brain in regulating these behaviors. Understanding the nature of these associations
is essential to breaking the cycle of alcohol misuse and violence.

Extent of the Alcohol-Violence
Association

Based on published studies,
Roizen (3) summarized the percentages of violent offenders who were drinking
at the time of the offense as follows: up to 86 percent of homicide offenders,
37 percent of assault offenders, 60 percent of sexual offenders, up to 57
percent of men and 27 percent of women involved in marital violence, and 13
percent of child abusers. These figures are the upper limits of a wide range
of estimates. In a community-based study, Pernanen (4) found that 42 percent
of violent crimes reported to the police involved alcohol, although 51 percent
of the victims interviewed believed that their assailantshad been
drinking.

Alcohol-Violence
Relationships

Several models have been
proposed to explain the complex relationships between violence or aggression
and alcohol consumption. To avoid exposing human or animal subjects to potentially
serious injury, research results discussed below are largely based on experiments
on nonphysical aggression. Other studies involving humans are based on epidemiological
surveys or data obtained from archival or official sources.

Alcohol Misuse
Preceding Violence

Direct Effects of
Alcohol. Alcohol may encourage aggression or violence by disrupting
normal brain function. According to the disinhibition hypothesis, for example,
alcohol weakens brain mechanisms that normally restrain impulsive behaviors,
including inappropriate aggression (5).By impairing information processing,
alcohol can also lead a person to misjudge social cues, thereby overreacting
to a perceived threat (6). Simultaneously, a narrowing of attention may lead
to an inaccurate assessment of the future risks of acting on an immediate
violent impulse (7).

Many researchers have
explored the relationship of alcohol to aggression using variations of an
experimental approach developed more than 35 years ago (8,9). In a typical
example, a subject administers electric shocks or other painful stimuli to
an unseen "opponent," ostensibly as part of a competitive task involving learning
and reaction time. Unknown to the subject, the reactions of the nonexistent
opponent are simulated by a computer. Subjects perform both while sober and
after consuming alcohol. In many studies, subjects exhibited increased aggressiveness
(e.g., by administering stronger shocks) in proportion to increasing alcohol
consumption (10).

These findings suggest
that alcohol may facilitate aggressive behavior. However, subjects rarely
increased their aggression unless they felt threatened or provoked. Moreover,
neither intoxicated nor sober participants administered painful stimuli when
nonaggressive means of communication (e.g., a signal lamp) were also available
(5,9).

These results are
consistent with the real-world observation that intoxication alone does not
cause violence (4). The following subsections explore some mechanisms whereby
alcohol's direct effects may interact with other factors to influence the
expression of aggression.

Social and Cultural
Expectancies. Alcohol consumption may promote aggression because people
expect it to (5). For example, research using real and mock alcoholic beverages
shows that people who believe they have consumed alcohol begin to act more
aggressively, regardless of which beverage they actually consumed (10). Alcohol-related
expectancies that promote male aggressiveness, combined with the widespread
perception of intoxicated women as sexually receptive and less able to defend
themselves, could account for the association between drinking and date rape
(11).

In addition, a person
who intends to engage in a violent act may drink to bolster his or her courage
or in hopes of evading punishment or censure (12,13). The motive of drinking
to avoid censure is encouraged by the popular view of intoxication as a "time-out,"
during which one is not subject to the same rules of conduct as when sober
(14,15).

Violence Preceding
Alcohol Misuse

Childhood Victimization.
A history of childhood sexual abuse(16) or neglect (17) is more likely
among women with alcohol problems than among women without alcohol problems.
Widom and colleagues (17) found no relationship between childhood victimization
and subsequent alcohol misuse in men. Even children who only witness family
violence may learn to imitate the roles of aggressors or victims, setting
the stage for alcohol abuse and violence to persist over generations (18).
Finally, obstetric complications that damage thenervous system at
birth, combined with subsequent parental neglect such as might occur in an
alcoholic family, may predispose one to violence, crime, and other behavioral
problems by age 18 (19,20).

Violent Lifestyles.
Violence may precede alcohol misuse in offenders as well as victims.
For example, violent people may be more likely than nonviolent people to select
or encounter social situations and subcultures that encourage heavy drinking
(21). In summary, violence may contribute to alcohol consumption, which in
turn may perpetuate violence.

Common Causes for
Alcohol Misuse and Violence

In many cases, abuse of
alcohol and a propensity to violence may stem from a common cause (22). This
cause may be a temperamental trait, such as a risk-seeking personality, or
a social environment (e.g., delinquent peers or lack of parental supervision)
that encourages or contributes to deviant behavior (21).

Another example of
a common cause relates to the frequent co-occurrence of antisocial personality
disorder (ASPD) and early-onset (i.e., type II) alcoholism (23).ASPD
is a psychiatric disorder characterized by a disregard for the rights of others,
often manifested as a violent or criminal lifestyle. Type II alcoholism is
characterized by high heritability from father to son; early onset of alcoholism
(often during adolescence); and antisocial, sometimes violent, behavioral
traits(24).Type II alcoholics and persons with ASPD overlap
in their tendency to violence and excessive alcohol consumption and may share
a genetic basis (23).

Spurious Associations

Spurious associations
between alcohol consumption and violence may arise by chance or coincidence,
with no direct or common cause. For example, drinking is a common social activity
for many adult Americans, especially those most likely to commit violent acts.
Therefore, drinking and violence may occur together by chance (5).In
addition, violent criminals who drink heavily are more likely than less intoxicated
offenders to be caught and consequently are overrepresented in samples of
convicts or arrestees (7).Spurious associations may sometimes be difficult
to distinguish from common-cause associations.

Physiology of Violence

Although individual behavior
is shaped in part by the environment, it is also influenced by biological
factors (e.g., hormones) and ultimately planned and directed by the brain.
Individual differences in brain chemistry may explain the observation that
excessive alcohol consumption may consistently promote aggression in some
persons, but not in others (25). The following subsections highlight some
areas of intensive study.

Serotonin

Serotonin, a chemical
messenger in the brain, is thought to function as a behavioral inhibitor.
Thus, decreased serotonin activity is associated with increased impulsivity
and aggressiveness (26) as well as with early-onset alcoholism among men (27).

Researchers have developed
an animal model that simulates many of the characteristics of alcoholism in
humans. Rhesus macaque monkeys sometimes consume alcohol in sufficient quantities
to become intoxicated. Macaques with low serotonin activity consume alcohol
at elevated rates (25); these monkeys also demonstrate impaired impulse control,
resulting in excessive and inappropriate aggression (25,27). This behavior
and brain chemistry closely resemble that of type II alcoholics. Interestingly,
among both macaques and humans, parental neglect leads to early-onset aggression
and excessive alcohol consumption in the offspring, again correlated with
decreased serotonin activity (27).

Although data are
inconclusive, the alcohol-violence link may be mediated by chemical messengers
in addition to serotonin, such as dopamine and norepinephrine (28). There
is also considerable overlap among nerve cell pathways in the brain that regulate
aspects of aggression (29), sexual behavior, and alcohol consumption (30).
These observations suggest a biological basis for the frequent co-occurrence
of alcohol intoxication and sexual violence.

Testosterone

The steroid hormone testosterone
is responsible for the development of male primary and secondary sexual characteristics.
High testosterone concentrations in criminals have been associated with violence,
suspiciousness, and hostility (31,32). In animal experiments, alcohol administration
increased aggressive behavior in socially dominant squirrel monkeys, who already
exhibited high levels of aggression and testosterone (33). Alcohol did not,
however, increase aggression in subordinate monkeys, which exhibited low levels
of aggression and testosterone (6).

These findings may
shed some light on the life cycle of violence in humans. In humans, violence
occurs largely among adolescent and young adult males,who tend to
have high levels of testosterone compared with the general population. Young
men who exhibit antisocial behaviors often "burn out" with age, becoming less
aggressive when they reach their forties (34). By that age, testosterone concentrations
are decreasing, while serotonin concentrations are increasing, both factors
that tendto restrain violent behavior (35).

Conclusion

No one model can account
for all individuals or types of violence. Alcohol apparently may increase
the risk of violent behavior only for certain individuals or subpopulations
and only under some situations and social/cultural influences(4,36).

Although much remains
to be learned, research suggests that some violent behavior may be amenable
to treatment and some may be preventable. One study found decreased levels
of marital violence in couples who completed behavioral marital therapy for
alcoholism and remained sober during followup(37). Results of another
study (7) suggest that a 10-percent increase in the beer tax could reduce
murder by 0.3 percent, rape by 1.32 percent, and robbery by 0.9 percent. Although
these results are modest, they indicate a direction for future research. In
addition, preliminary experiments have identified medications that have the
potential to reduce violent behavior. Such medications include certain anticonvulsants
(e.g., carbamazepine) (38); mood stabilizers (e.g., lithium) (39); and antidepressants,
especially those that increase serotonin activity (e.g., fluoxetine) (40,41).
However, these studies either did not differentiate alcoholic from nonalcoholic
subjects or excluded alcoholics from participation.

Both alcohol use
and violence are common in our society, and there are many associations between
the two. Understanding the nature of these associations, including the environmental
and biological antecedents of each and the ways in which they may be related,
is essential to developing effective strategies to prevent alcohol-related
violence as well as other social problems, such as domestic violence, sexual
assault, and childhood abuse and neglect. Because no area of science stands
apart from another, understanding more about alcohol-related violence also
will shed light on violence in general and produce information that may be
useful to reducing it.

Science has made progress
on elucidating the environmental and biological antecedents of alcohol abuse
and alcoholism; less progress has been made toward understanding the causes
of violence. Understanding the biology of violence will help us to clearly
define the role of the environment in increasing the risk for violence and
increase our understanding of who is at risk for violent behavior. This understanding
also will help us to develop effective interventions--both social and medical
where intended--to help those whose violence has caused trouble for themselves
and others.